Steam Table Add-on Instructions for Logix. Programmable Automation
Controllers. Steam provides process heating, pressure control, mechanical drive,
and.
Steam Table Add-on Instructions for Logix Pre-Programmed and Pre-Tested
Features and Benefits • Helps eliminate the need for a separate computer which has been traditionally needed due to the complexity of these calculations • Helps eliminate the need to plot steam temperature and pressure on Mollier diagram to determine enthalpy and entropy • Provides a cost effective solution for smaller steam system skids that require only limited I/O and a small controller to operate • Helps save programming time by allowing for creation of commonly used custom instructions • Promotes consistency between projects – no need to constantly re-invent commonly used control algorithms • Helps reduce debugging time by animating the values in logic for a specific call to the instruction • Helps protect intellectual property, diminishing the possibility of IP being changed/copied
Steam provides process heating, pressure control, mechanical drive, and component separation, as well as water for many process reactions. It has performance advantages that make it an indispensable means of delivering energy including ease of transportability, high efficiency, high heat capacity, and low cost with respect to the other alternatives. As a critical part of an infrastructure, end users of steam systems look to measure their efficiency. They also need to gather critical information to better determine what steam equipment could be optimized, cleaned or potentially replaced to gain the highest return on investment.
Region Key: • 1 - Water • 2 - Super Heated • 3 - Super Critical • 4 - Saturation Line • 5 - High Temperature
Five Region Steam Table
Steam Table Add-On-Instruction Rockwell Automation® offers a complete set of calculation-based, steam table Add-On Instructions for the Allen-Bradley® Logix family of programmable automation controllers. These steam table Add-On Instructions (blocks) allow you to quickly gather information, using standard measurements, across all five regions of the steam table. You can determine properties such as enthalpy, entropy, specific volume of wet steam (saturated), and dry steam. Users can configure all blocks to work in the International System of Units or English units. The International Association for the Properties of Water and Steam Industrial Formulation 1997 (IAPWS-IF97) steam table Add-On Instructions use inherent ready-to-use tags and provide code for the Logix controller.
By implementing these pre-programmed, pre-tested Rockwell Automation Process Objects, you can dramatically reduce the amount of time required to configure and commission your steam equipment, as well as provide better information to operators making it easier to operate and troubleshoot. General Steam Table Add-On Instructions
General Steam Table Block
Reverse Steam Table Add-On Instructions
Reverse Steam Table Blocks
Saturation Add-On Instructions
The general Add-On Instruction is based on pressure and temperature as input parameters and returns enthalpy, entropy, specific volume and region number. The Add-On Instruction automatically and dynamically calculates the region based on pressure and temperature and creates a seamless transition across all regions. Since this capability exists on small, inexpensive CompactLogix™ controllers, you no longer need to purchase an expensive Distributed Control System (DCS) or to run calculations on a separate computer and feed the data back into the control system. This dynamic capability increases the financial feasibility for all skid systems. Typical applications include energy or efficiency calculations for turbines, pasteurizers, sterilizers, cookers/retorts, evaporators, heat exchangers and other steam consuming skid equipment.
Three reverse steam table Add-On Instructions calculate water and steam properties that are based on pressure and entropy (p,s), pressure and enthalpy (p,h), and enthalpy and entropy (h,s). The reverse equations are valid for Regions 1 through 4 on the Steam Table. The Add-On Instructions automatically and dynamically calculate the region based on the input values and creates a seamless transition across all regions. These blocks are of special interest to energy-related applications: calculations for heat and power cycles, boilers, feed pumps, steam turbines, hydro-turbines, and similar equipment.
Saturation Blocks Rockwell Automation has two blocks that are used specifically for saturation. The first is used for calculating super heat temperatures. It takes the pressure of the process as an input and returns the temperature point on the saturation line. By measuring temperature, the super heat temperature can be quickly calculated (process temperature minus the saturation temperature equals super heat temperature. The second block takes temperature as its input and returns pressure on the saturation line.
Mollier Diagram
Add-On Instructions in Use Many engineers that deal with utilities and steam use the Mollier Diagram to provide a graphical representation of their steam process. The Steam Table Add-On Instructions virtually eliminate the need to plot steam temperature and pressure on the Mollier Diagram to determine enthalpy and entropy. Instead, the Add On Instructions provide these values dynamically. The following examples detail additional ways the Add-On Instructions can be used in different types of applications.
Example 1: Heat exchanger with steam on one side and liquid on the other Requirement: Heat the liquid to a particular temperature. By measuring the inlet and outlet pressure and temperature of the steam, and by knowing flow, you can calculate the steam enthalpy drop across the heat exchanger. With the measurement of the liquid temperature, delta, and the flow rate, you can determine how much energy is transferred into the liquid and the efficiency of the heat exchanger. Through periodic monitoring, you can now determine when efficiency is dropping and take appropriate actions. Example 2: Steam Injection and a recipe that uses water as one of the ingredients Requirement: Heat the mixture with direct steam injection. To determine the amount of steam to be added and the length of time, you will want to know the temperature of the steam. Since steam will be used as the source of heat and also one of the ingredients (water), it is important to measure the specific volume of the steam. With the steam Add-On Instruction, you to ensure better recipe consistency from plant to plant, as well as from batch to batch within a plant. Example 3: A simple generation facility where a biomass boiler is generating steam for a turbine. Requirement: Calculate the energy in a steam system. It is possible to calculate the energy in the steam being created in the closed loop. Then, by knowing how much electricity is being generated, you can calculate the amount of energy in the steam being produced versus the energy in the electricity. This is valuable when looking at a boiler as the fuel characteristics change and how it affects the output of the generator. Also, you can calculate the actual turbine efficiency using these tables. Example 4: An electrical power plant with a steam turbine. Requirement: To calculate the isentropic efficiency of the turbine given input and output pressure and temperature. Use the the standard P_Steam block to determine the enthalpy and entropy values for the input (state 1). With the output side (state 2), you can calculate both the isentropic enthalpy and the actual enthalpy. Calculate the actual enthalpy using the standard P_Steam block. Use the reverse block P_Steam_ps for isentropic enthalpy. Since the end of the isentropic process will exist as a saturated mixture, it is necessary to find the steam quality. Then, use the reverse block P_Steam_ps and the quality factor to calculate the final isentropic enthalpy. Finally, you can calculate the isentropic efficiency using the 2a standard formula: hh11-h -h2s , where h1-h2a is the actual enthalpy and h1-h2s is the isentropic efficiency.
Allen Bradley, CompactLogix, PlantPAx, are trademarks of Rockwell Automation, Inc. Trademarks not belonging to Rockwell Automation are property of their respective companies.
Publication PROCES-AP052B-EN-E - September 2015 Supersedes Publication PROCES-AP052A-EN-E October 2011
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